1. Field of the Invention
This invention is concerned with a method of neutralizing an alkaline catalyst used to polymerize polydiorganosiloxane.
2. Background Information
Diorganocyclosiloxane or linear polydiorganosiloxane is polymerized by heating with ring opening or condensation catalysts such as strong acids or bases. Among the most common alkaline catalysts are alkali metal compounds such as potassium hydroxide, sodium hydroxide, cesium hydroxide, and potassium silanolate. After polymerization, the alkaline catalyst is neutralized with a material such as trimethylchlorosilane, trichloroethyl phosphite, phosphorus pentoxide, silyl phosphate, acetic acid or carbon dioxide.
U.S. Pat. No. 4,439,592, issued Mar. 27, 1984, to Maass et al. teaches the preparation of polydiorganosiloxanes having terminal triorganosilyl groups. A process is described in which, before polymerization, part of the cyclic diorganosiloxane is distilled off in the presence of the polymerization catalyst at a temperature at least 10.degree. C. below the temperature at which polymerization begins.
U.S. Pat. No. 4,551,515, issued Nov. 5, 1985, to Herberg et al. teaches that a mixture of cyclopolysiloxane monomers and chainstopping agents is preferably passed through a drying means to eliminate water from the mixture, because water will terminate or chainstop diorganopolysiloxane polymer with silanol groups and thus reduce the viscosity of the polymer and change the nature of its interaction with a filler. They further teach that after thorough neutralization of the catalyst after polymerization, the polymer can be devolatilized to remove volatiles such as unreacted cyclopolysiloxanes.